function EventEmitter() {
  this.listener = [];
}

EventEmitter.prototype = {
  constructor: EventEmitter,
  addEventListener: function (event, callback) {
    console.log(this);
    this.listener.push({
      key: event,
      callback: callback
    });
  },
  removeEventListener: function (event) {

  }
};

const foo = new EventEmitter();
const foo2 = new EventEmitter();

foo.addEventListener('click',function(){
  console.log('click');
});

console.log(foo);
console.log(foo2);
